Syrian government forces entered a key northwestern town on Sunday amid intense fighting with militants and their rebel allies that has left dozens of combatants dead, a war monitor said.

The Syrian Observatory for Human Rights reported "fierce clashes" as it said government ground troops penetrated Khan Sheikhun in Idlib province for the first time since they lost control of it in 2014.

The latest fighting, which broke out overnight Saturday to Sunday, has already killed at least 59 militants and allied rebels as well as 28 members of pro-government forces, the UK-based monitor said.

Pro-government forces have been advancing over the past few days in a bid to encircle Khan Sheikhun from the north and west and to seize a key highway.

The Syrian Observatory for Human Rights reported “fierce clashes” as it said regime ground troops penetrated Khan Sheikhun in Idlib province for the first time since they lost control of it in 2014.https://t.co/VtVdiNDgn8

The road runs through Idlib, connecting government-held Damascus with the northern city of Aleppo, which the government took back from rebels in December 2016 after a pulverising Russian-backed air offensive.

Now almost emptied of inhabitants, Khan Sheikhun sheltered almost 100,000 people before the start of the current military escalation, the majority displaced from Hama province.

"Many of these people have been displaced up to five times," the UN's regional spokesman for the Syria crisis, David Swanson, told AFP on Saturday.

"Ongoing clashes, shelling and air strikes, including the use of barrel bombs, continue unabated" and have damaged schools and hospitals, he added.

Ahead of the expected government assault, Khan Sheikhun residents have fled to the relative safety of areas farther north. During recent nights, the Syria Civil Defence workers known as the White Helmets helped evacuate the remaining families, the Defense Post website reported.

“The children were so afraid,” Hamid Qutini, a search-and-rescue volunteer, said. “We gave them cookies and tried to assure them that we would take them far away from the sounds of the explosions.”

Families in need of transport flagged the White Helmets down in their neighbourhoods or contacted them on the online messaging service WhatsApp. Qutini describes seeing scores of frightened children, many of them orphans, clutching their blankets and pillows.

“This isn’t their fault,” Qutini said. “I felt so helpless that I couldn’t stop the bombings for them.”

Under the cover of darkness, Qutini and other volunteers drove the families to neighbouring al-Dana, Atmeh and Idlib city.

With the nearby Turkish border closed to refugees, many of the displaced are now living in olive groves and sheltering beneath trees. Others are packed into overcrowded displacement camps

On Sunday, government forces took the village of Tel al-Nar and nearby farmland northwest of Khan Sheikhun before closing in on the town, Observatory head Rami Abdel Rahman said.

They then advanced into the northwestern districts of the town amid "ferocious resistance" from militants and allied rebels, he said.

Militant group Hayat Tahrir al-Sham (HTS), led by Syria's former al-Qaeda affiliate, carried out several suicide bombings to slow the advance of government troops, Abdel Rahman added.

HTS controls most of Idlib province as well as parts of the neighbouring provinces of Hama, Aleppo and Latakia.

A buffer zone deal brokered by Russia and Turkey last year was supposed to protect the Idlib region's three million inhabitants from an all-out government offensive, but it was never fully implemented.

Government and Russian air strikes and shelling since late April have killed more than 860 civilians, according to the Observatory, which relies on sources inside Syria for its information.

On Sunday, air strikes by the Syrian government and its ally Russia killed two people, including a child, in the south of Idlib, the Observatory said.

Heavy losses

More than 1,400 rebels and 1,200 pro-government forces have been killed since April, according to the monitor.

Naji Mustafa, a captain in the National Liberation Army rebel group, told MEE earlier this week that despite the Syrian government's gains, Bashar al-Assad's forces were taking heavy losses.

The violence has displaced more than 400,000 people, the UN says.

Khan Sheikhun was hit by a chemical attack that killed more than 80 people in April 2017, attributed to the Syrian government by the UN and international experts.

In response, US President Donald Trump ordered strikes on the government's key Shayrat airbase.

Syria's conflict has killed more than 370,000 people and displaced millions at home and abroad since starting with the brutal repression of anti-government protests in 2011.